The input children receive is a critical factor in their language development, but much of the language they hear directed to themselves and others occurs in noisy or multi-talker environments. Yet children must rely on these degraded signals to attempt to learn their native language. The language learning systems of the brain evolved in what were presumably far quieter ambient environments than present-day settings, where noise from traffic, television, and electronic devices are ubiquitous. Recent work suggests that children are affected by background noise much more than are adults, potentially limiting the extent to which they can benefit from the language input they receive. Yet the underlying reason for these age-related differences remains unclear, as is the effect that such differences actually have on learning. Noise has a substantial public health impact, ranging from sleep disturbance and stress to decreased performance in school. Noise and other unwanted auditory signals can potentially affect speech processing in at least two ways: they can degrade the quality of the target signal (e.g., by making portions of it inaudible) and they can serve as a potential source o distraction or interference. We predict that the latter plays a larger role in young children's particular difficulty with noise, and that this is tied to children's developing attention abilitie in general. To examine this, the current proposal has three specific aims: i) to distinguish effects caused by the degradation of the signal from effects of distraction, and identify which factor plays the greater role in children's perceptual difficulties, and how this relates to other nonlinguistic attentional skills (specifically selective attention in the presence of distractors);ii) to investigate the range of stimuli for which young children show effects of distraction; and iii) to investigate the effects of noise on the learning of new words, not just recognition of already-known words. Distinguishing effects of signal degradation from effects of distraction has both theoretical and applied significance. Theoretically, understanding the nature of children's difficulties provides insight into the mechanisms involved in speech perception, as well as into the nature of speech processing development. Moreover, most theories of early language learning presume either that the child is hearing language input in ideal listening conditions or that the input has already been separated from background noise. The proposed studies will thus spur the development of more nuanced views of language acquisition, and provide critical information for evaluating and improving such models. On an applied level, understanding the limitations of children's ability to understand and learn from spoken language in the context of other speech will have vital implications for child-rearing practices, and for understanding potential causes for language delay. The results from these studies will also impact how we think about intervention and the effect of child care quality.